This invention relates to an apparatus for thermally conditioning heat softenable material such as glass, and more specifically, to an auxiliary heated bushing block for feeding heat softenable glass to a stream feeder or bushing in a manner that thermally conditions the glass.
In a typical direct melt operation, glass batch is reduced to a molten state and refined in a furnace. The refined glass is flowed through a forehearth channel to openings in the bottom of the channel. The glass flows downwardly through the openings to electrically heated stream feeders or bushings disposed in spaced relation along the forehearth. Streams of glass flow through orifices in the bushings, and the streams are attenuated to filaments or fibers by well known methods.
A temperature gradient is produced in the molten glass as it flows through the opening in the forehearth downward into the bushing. The bushing, being generally rectangular in shape, tends to radiate heat from the ends more rapidly than at the center. The difference in temperature of the glass at the bushing block and the glass at the center of the passage in the bushing block can be 100.degree. F. or more. Such glass, having a large temperature gradient, entering a bushing during the operation of the fiber forming process, can cause a non-uniform heat pattern across the bottom plate of the bushing and an inefficient fiber forming operation. Such glass entering a fiber forming bushing can result in the production of fibers which do not meet process specifications and can result in process interruptions.
Various schemes have been devised to attempt to ensure that the glass being fed to a fiber forming bushing has a uniform temperature distribution. Greene et al, U.S. Pat. No. 4,161,396, teaches various geometrical configuration for flow blocks to minimize the heat losses due to these flow blocks. Babbitt, U.S. Pat. No. 4,270,941, teaches the use of heat pipes located in the opening of a flow block to attempt to make the temperature of the molten material uniform across the opening. Further investigation has shown, however, that by selectively applying heat to the molten material as it flows through a bushing block, especially at the ends, a more efficient method of ensuring that the molten material, as it exits a bushing, will produce uniform fiber diameters across the width of the bushing.